Electrified fences



1952 J. LEGRAND 3,051,449

ELECTRIFIED FENCES Filed Nov. 14, 1958 Maw? JE ZEc-RAND 21 WM $41M;

United States Patent Office 3,051,449 Patented Aug. 28, 1962 3,051,449 ELECTRIFIED FENCES Jean Legrand, 8 Rue Jules Gautier, Nanterra, France Filed Nov. 14, 1958, Ser. No. 773,905 Claims priority, application France Nov. 19, 1957 12 Claims. (til. 256-10) The present invention relates to electrified fences and has for an object a particularly effective electrical fence which is not similar to fences for enclosing cattle, either in construction or in the manner in which it is electrified, nor yet in its control, signalling or warning attachments. It is another object of the invention to produce an electrified fence suitable for ensuring the defence of a position subject to enemy attacks or to protect a frontier the crossing of which is feared. It is a further object to produce such a fence adapted to frustrate attempts at sabotage or destruction thereof.

Instead of a protection limited to one or two levels by one or two conductors electrified by pulses, the fence which is the object of the invention comprises a protection having a number of levels, ensured by as many separate and distinct electrified conductors, bet-ween which are disposed conductors which are interconnected and also connected to earth. Between the first and the second conductor, are applied, instead of pulses of direct current of only a few millicoulombs, electrical oscillations derived from any suitable source of alternating current, suitably introduced by means of transformers or auto-transformers having separate functions and producing different voltages. Thus, from any alternating voltage input an alternating current can be produced whose voltage reaches a few thousand volts, for example 3,000 to 5,000 volts, which serves for the electrification of the fence, by using a step up transformer.

Transformers operate at relatively low voltage levels and their constants and connections are designed to exert the necessary control on the operation of the fence, detection and signalling devices being added to them in order, to detect and indicate by any suitable visible or audible warning means when any abnormality in the state of the fence occurs. Cutting of the wires, contact between conductors or to ground, or defective insulation are the main abnormalities to be guarded against. For most of these controls it is sufiicient to use the low voltage devices referred to above, except for the high voltage transformer for electrification, but for a part of the necessary controls this main transformer and the high voltage circuits fed by it must be used.

In order that the characteristics and advantages of the invention may be better understood, reference will now be made to a specific embodiment thereof in the accompanying drawing, comprising an electrified fence section which must be energised and controlled to meet the very special requirements which will be indicated (hereinafter. Both high and low voltage components are shown in the drawing.

The common source of electrical energy is represented in the drawing by an auto-transformer 12 energised from any suitable alternating current source that provides two voltages at the terminals 10 and 11.

An ammeter 13 is common to two circuits connected to the auto-transformer. The control current circuit leads through the protection reactance 14, to the primary 8 of an input transformer having a secondary winding 5 for providing the control current for the fence.

The current for the high voltage electrification is provided by a step-up transformer 15 whose primary can be switched in by a switch 16 (having a detachable handle by way of precaution) and is in series with the protection inductance 17.

The secondary of the step-up transformer 15 has its upper terminal connected to a tap 9 on the secondary winding 5 by means of a well insulated conductor and a neon lamp 18 gives an indication of its operation. The lamp goes out when the voltage at the terminals of the secondary of transformer 15 drops below a certain value. A multiple contact switch 19 allows by selecting one of the multiple tappings on the secondary of the transformer, a suitable voltage to be applied 180 out of phase with the the voltage applied to the insulated wires of the fence section to one of the terminals of the compensating condenser 20 that has a suitable value. The compensating condenser 20 has the other of its terminals connected to ground through a cut-off button 21.

Since the general insulation of the fence is best tested by applying a selected high voltage thereto, the drawing shows the connection of the step-up transformer 15 for this purpose. A relay 23 is connected in a conductor 22 which leads to a second grounding point at Z; the sensitivity of this relay is variable by means of a potentiometer. If the general insulation diminishes, the coil of the relay 23, which energises at a maximum, attracts its armature 24 and causes it to efiect a bridge between the conductor 25, connected to one of the terminals of the feed source, and the conductor 26: a warning lamp 28 connects the conductor 26 to a conductor 27 connected to the opposite terminal of the feed source. The lamp 28 may be coloured red.

A bell 30 which is already connected by one of its terminals to the conductor 27 may be connected by its other terminal, to a conductor 29 through a switch 31;

at that moment the conductor 26 connects the conductor 29 to the opposite feed conductor 25. Above the bell 30 are provided fuses 32 and terminals 33 which may feed other warning devices.

The installation shown in the drawing has been designed to satisfy very stringent requirements, and it is of interest to give details thereof herebelow:

(l) The state of the electrified section 12--34 must be controlled from the electrifying apparatus itself. For this purpose there are provided the two transformers 58 and 7-34, transformer 58 being an input transformer, and transformer 734 being an output transformer, and an auto-transformer 6 at the end of the section.

These transformers are low voltage transformers. They enable voltage differences to be maintained between the wires ll234 such that an intentional or chance contact between any two or these wires, which are insulated with respect to ground at Z, is detected as a consequence of the disengagement of the movable armature of the primary relay 35 which energises at a minimum and controls the secondary winding 39. The latter is energised as a result of the armature attraction in the conditions which have just been mentioned, when an abnormal contact with the fence occurs, or the fence is cut, to cause the release of the main relay 23.

By a conducting bridge which is then established by a palette of this secondary relay, a maintenance circuit for energising the coil 39 closes automatically when the armature 24 of the relay 23 sticks and the function of the relay 23 and the connections thereof have been described above.

The button 38 is provided to de-energise the relay 39 and the but-ton 36 is provided for deenergising the control relay of the electrified fence section, when desired.

In order to give a visual indication of what has occurred, a warning lamp is connected at 37, said lamp lighting up and remaining lighted for the duration of the defect detected. This lamp 37 may be coloured green to differentiate it from the lamp 28.

(2) It is required that the apparatus shall supply a voltage which is high relatively to ground, that it shall also compensate the considerable dephasing created by the abnormally high capacity of the fence, and that finally it shall ensure the protection of the whole apparatus in the event of the earthing of a wire brought to a high voltage.

For this requirement it is sufficient to insert the induc tance 17 in the primary circuit of the high voltage step-up transformer 15 in series with the ammeter 13 and provide the switch 16 with a detachable handle.

(3) In order to satisfy the need for safety, which is just as imperative, the apparatus must detect in a practical manner an insulation defect, even if it is only of a transitory nature, between the high voltage conductors and earth.

It is necessary that it be possible to adjust the sensitivity threshold. The relay 23 has an important part to play and its winding must be spared the effects of any abnormal excess voltage. Therefore arrangements have been made so that the actuating current of the relay 23 is the only current in phase, and that a different path is followed by the out of phase current by means of the condenser 20 which has the function of a true capacity compensator.

In order to give an idea of the performance rendered possible by the means of the present invention I have found that, with an out of phase current of 250 millianrps (or even 00 milliamps), it is easily possible to detect an in-phase current of the order of only 25 milliamps. In other words it has been possible, on an impedance line equal to 10,000 ohms relative to earth, to detect an insulation defect of 100,000 ohms.

To the control devices connected in the vicinity of the electrifier are added control buttons whose reference numorals and functions are as follows:

Button 36 controls the detection relay 35 (detecting cutting or bridging of the fence wires).

Button 21 controls the relay 23 (detection of insulation defects).

Button 38 enables the general signalling relay to be restored to normal.

Button 31 serves to cut or to establish the audible signal at will.

Reference numeral 19 is the change-over switch serving for controlling the compensation and de-phasing.

'I claim:

1. An electrified fence arrangement comprising a fence section comprising a plurality of groups of conductors, each group consisting of three spaced conductors the outer one of which are inductively coupled and fed from the primary of a transformer and respectively connected by an auto-transformer, and the central ones of which spaced conductors are interconnected and respectively connected to ground.

2. An electrified fence arrangement comprising a fence section comprising four live conductors, a step-up transformer having a primary winding and a secondary winding, a grounded conductor between each adjacent pair of said live conductors, means connecting said secondary winding to two of said live conductors, means inductively connecting said two live conductors to the other two live conductors, means connecting all said grounded conductors together and to ground, and electrical conductors connected between said primary winding of said step-up transformer and a source of alternating current.

3. An arrangement as claimed in claim 2, comprising further an output transformer, and means for connecting the primary winding of said output transformer to said other two live conductors.

4. An arrangement as claimed in claim 2, comprising further a variable-sensitivity relay connected to said secondary winding of said transformer, warning devices connected to said variable-sensitivity relay and control means for breaking and re-establishing the circuits interconnecting said transformer and said warning devices.

5. An electrified fence arrangement comprising four live conductors arranged in a closed circuit, a first transformer device connected to two of said conductors and forming a first group, for injecting between said two conductors a low voltage current, an auto-transformer connected to the other two of said four conductors forming a second group, means for connecting said conductors forming said first group to said auto-transformer, an out put transformer connected to said second group of con ductors, a relay device, means connecting said output transformer to said relay device, said relay operating on a minimum, and a warning device connected to said relay.

6. An electrified fence arrangement comprising a fence section that consists of two groups of conductors, each of said groups consisting of three spaced conductors, an input transformer having a secondary winding, one end of each of the outer ones of a first group of said conductors being connected to said secondary winding, means inductively connecting the other end of said outer ones of said first group of conductors to one end respectively of the outer ones of a second group of said conductors, an output transformer having a primary winding, the other ends of said outer ones of said second group of conductors being connected to said primary of said output transformer, and the third conductor of each of said groups being connected together and to ground.

7. An electrified fence arrangement comprising a fence section that consists of two groups of conductors, each of said groups consisting of three spaced conductors, an input transformer having a secondary winding, one end of each of the outer ones of a first group of said conductors being connected to said secondary winding, means inductively connecting the other end of said outer ones of said first group of conductors to one end respectively of the outer ones of a second group of said conductors, an output transformer having a primary winding and a secondary winding, the other ends of said outer ones of said secondary group of conductors being connected to said primary of said output transformer, the third conconductor of each of said groups being connected together and to ground, a warning device, and a minimum-currentresponsive relay connected between said warning device and the secondary Winding of said output transformer.

'8. An electrified fence arrangement comprising a fence section that consists of two groups of conductors, each of said groups consisting of three spaced conductors, an input transformer having a primary winding and a secondary winding, one end of each of the outer ones of a first group of said conductors being connected to said secondary winding, means inductively connecting the other end of said outer ones of said first group of conductors to one end respectively of the outer ones of a second group of said conductors, an output transformer having a primary winding and a secondary winding the other ends of said outer ones of said second group of conductors being connected to said primary of said output transformer, the third conductor of each of said groups being connected together and to ground, a first Warning device, a minimum-current-responsive relay connected between said first warning device and said secondary winding of said output transformer, a second Warning device, and a maximum-current-responsive relay connected between said second warning device and said primary winding of said input transformer.

9. An electrified fence arrangement comprising four conductors arranged in a closed circuit, an input transformer at one end of said closed circuit, an output transformer at the other end of said closed circuit, each of said transformers being respectively connected to the one ends of a pair of said conductors, an auto-transformer connected to the other ends of both pairs of conductors, a minimum-functioning relay connected to the secondary winding of said output transformer, a grounding conductor located between the two conductors of each of said pairs of conductors, and a further grounding conductor between the said pairs of conductors, all three of said grounding conductors being connected together by their ends and commonly to ground.

10. An electrified fence arrangement comprising four conductors arranged in a closed circuit, an input transformer at one end of said closed circuit, an output transformer at the other end of said closed circuit, each of said transformers being respectively connected to the one ends of a pair of said conductors, an auto-transformer connected to the other ends of both pairs of conductors, a minimum-functioning relay connected to the secondary winding of said output transformer, a grounding conductor located between the two conductors of each of said pairs of conductors, a further grounding conductor between the said pairs of conductors, all three of said grounding conductors being connected together by their ends and commonly to ground, and a step-up transformer having its secondary Winding connected to the secondary winding of said input transformer.

11. An electrified fence arrangement as claimed in claim 10 and comprising further, a relay whose sensitivity is adjustable, connected to the secondary winding of said step-up transformer, visual and audible warning devices connected in circuit to be operated by said relay, and switch means connected in circuit for cutting out and for re-stabilising said warning devices into the operable condition.

12. An electrified fence arrangement as claimed in claim 11, in which said step-up transformer has a multitapped secondary winding, and comprising further, a multi-position switch selectively connectible to one of the taps on said secondary winding, a condenser connected in series between the common pole of said switch and ground, and a press-button switch connected in the line between said condenser and ground.

References Cited in the file of this patent UNITED STATES PATENTS 1,436,926 Williams \Nov. 28, 1922 2,215,718 Sch'aefer Sept. 24, 1940 2,364,994 Moore Dec. 12, 1944 2,567,667 Hanchett Sept. 11, 1951 FOREIGN PATENTS 1,142,674 France Sept. 20, 1957 

